METHODS OF FORMING A NONVOLATILE MEMORY CELL AND METHODS OF FORMING AN ARRAY OF NONVOLATILE MEMORY CELLS
A method of forming a nonvolatile memory cell includes forming a first electrode and a second electrode of the memory cell. Sacrificial material is provided between the first second electrodes. The sacrificial material is exchanged with programmable material. The sacrificial material may additionally be exchanged with select device material.
Embodiments disclosed herein pertain to methods of forming a nonvolatile memory cell and to methods of forming an array of nonvolatile memory cells.
BACKGROUNDMemory is one type of integrated circuitry, and is used in computer systems for storing data. Such is usually fabricated in one or more arrays of individual memory cells. The memory cells might be volatile, semi-volatile, or nonvolatile. Nonvolatile memory cells can store data for extended periods of time, in many instances including when the computer is turned off. Volatile memory dissipates and therefore requires being refreshed/rewritten, in many instances multiple times per second. Regardless, the smallest unit in each array is termed as a memory cell and is configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Integrated circuitry fabrication continues to strive to produce smaller and denser integrated circuits. Accordingly, the fewer components an individual circuit device has, the smaller the construction of the finished device can be. Likely the smallest and simplest memory cell will be comprised of two current conductive electrodes having a programmable material received there-between. The programmable material is selected or designed to be configured in a selected one of at least two different states to enable storing of information by an individual memory cell. The reading of the cell comprises determination of which of the states the programmable material is in, and the writing of information to the cell comprises placing the programmable material in a predetermined state. Some programmable materials retain a state in the absence of refresh, and thus may be incorporated into nonvolatile memory cells.
Some programmable materials may contain mobile charge carriers larger than electrons and holes, for example ions in some example applications. Regardless, the programmable materials may be converted from one memory state to another by moving the mobile charge carriers therein to alter a distribution of charge density within the programmable materials. Some example memory devices that utilize ions as mobile charge carriers are resistive RAM (RRAM) cells, which can include classes of memory cells containing multivalent oxides, and which can include memristors in some specific applications. Other example memory devices that utilize ions as charge carriers are programmable metallization cells (PMCs); which may be alternatively referred to as a conductive bridging RAM (CBRAM), nanobridge memory, or electrolyte memory.
The RRAM cells may contain programmable material sandwiched between a pair of electrodes. The programming of the RRAM cells may comprise transitioning the programmable material between first a memory state in which charge density is relatively uniformly dispersed throughout the material and a second memory state in which the charge density is concentrated in a specific region of the material (for instance, a region closer to one electrode than the other).
A PMC may similarly have programmable material sandwiched between a pair of current conductive electrodes. The PMC programmable material comprises ion conductive material, for example a suitable chalcogenide or any of various suitable oxides. A suitable voltage applied across the electrodes generates current conductive super-ionic clusters or filaments. Such result from ion transport through the ion conductive material which grows the clusters/filaments from one of the electrodes (the cathode), through the ion conductive material, and toward the other electrode (the anode). The clusters or filaments create current conductive paths between the electrodes. An opposite voltage applied across the electrodes essentially reverses the process and thus removes the current conductive paths. A PMC thus comprises a high resistance state (corresponding to the state lacking a current conductive filament or clusters between the electrodes) and a low resistance state (corresponding to the state having a current conductive filament or clusters between the electrodes), with such states being reversibly interchangeable with one another.
Other example programmable materials are organic, for example which may change between or among memory states by switching via localized redox reactions, charge transfer reactions, or electronic transitions. Examples include certain polymers, self-assembled molecular monolayers, carbonaceous materials, organic-metal complexes, and blends or layered stacks thereof.
Example embodiments of a method of forming a nonvolatile memory cell, including forming an array of such cells, is initially described with reference to
Substrate 10 comprises a suitable base substrate 12 which may be homogenous or non-homogenous, for example comprising multiple different composition materials and/or layers. As an example, such may comprise bulk monocrystalline silicon and/or a semiconductor-on-insulator substrate. As an additional example, such may comprise dielectric material having conductive contacts or vias formed therein which extend vertically or otherwise into current conductive electrical connection with electronic device components, regions, or material received elevationally inward of the dielectric material. In this document, vertical is a direction generally orthogonal to a primary surface relative to which the substrate is processed during fabrication and which may be considered to define a generally horizontal direction. Further, “vertical” and “horizontal” as used herein are generally perpendicular directions relative one another independent of orientation of the substrate in three dimensional space. Further in this document, “elevational” and “elevationally” are with reference to the vertical direction from a base substrate upon which the circuitry is fabricated, for example, base substrate 12.
A plurality of horizontally oriented first electrode lines 16 is received over base substrate 12. Dielectric material 14 is also received over base substrate 12 between first electrode lines 16. Electrode lines 16 comprise current conductive material and may be homogenous or non-homogenous. In the context of this document, “current conductive material” is a composition where electric current flow would inherently occur therein predominantly by movement of subatomic positive and/or negative charges when such are generated, as opposed to predominantly by movement of ions. Example current conductive materials are elemental metals, alloys of elemental metals, current conductive metal compounds, and conductively doped semiconductive material, including any combinations thereof. Example suitable dielectric material 14 includes silicon nitride and doped or undoped silicon dioxide, such as boron/or phosphorous doped silicate glasses. Dielectric material 14 may be homogenous or non-homogenous. First electrode lines 16 with dielectric material 14 there-between may be fabricated by any existing or yet-to-be-developed manner(s). Subtractive patterning and etch, and/or damascene-like methods are but two examples.
Dielectric material 18 and sacrificial material 20 have been formed over base substrate 12. Each may be homogenous or non-homogenous, and dielectric material 18 may be the same as or different from composition(s) of dielectric material 14. Sacrificial material 20 may be any one or combination of electrically insulative, electrically conductive, and semiconductive. In the
Still referring to
Hard-masking material 24 and patterning material 26 have been formed elevationally outward of current conductive material 22. Each may be homogenous or non-homogenous, with an example hard-masking material being silicon nitride and an example patterning material being photoresist.
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One example programmable material is ion conductive material. Example suitable such materials comprise chalcogenide-type (for instance, materials comprising one or more of germanium, selenium, antimony, tellurium, sulfur, copper, etc.; with example chalcogenide-type materials being Ge2Sb2Te5, GeS2, GeSe2, CuS2, and CuTe) and/or oxides such as zirconium oxide, hafnium oxide, tungsten oxide, copper oxide, niobium oxide, iron oxide, silicon oxide (specifically, silicon dioxide), gadolinium oxide, etc. capable of inherently (or with additive) supporting electrolyte behavior. Such may have silver, copper, cobalt, and/or nickel ions, and/or other suitable ions, diffused therein for ionic conduction, analogously to structures disclosed in U.S. Pat. No. 7,405,967 and U.S. Patent Publication Number 2010/0193758.
Additional example programmable materials include multi-resistive state metal oxide-comprising material. Such may comprise, for example, at least two different layers or regions generally regarded as or understood to be active or passive regions, although not necessarily. Alternately, such may only comprise active material. Example active cell region compositions which comprise metal oxide and can be configured in multi-resistive states include one or a combination of SrxRuyOz, RuxOy, and InxSnyOz. Other examples include MgO, Ta2O5, SrTiO3, SrZrO3, BaTiO3, Ba(1-x)SrxTiO3, ZrOx (perhaps doped with La), and CaMnO3 (doped with one or more of Pr, La, Sr, or Sm). Example passive cell region compositions include one or a combination of Al2O3, TiO2, and HfO2. Regardless, a programmable material composite might comprise additional metal oxide or other materials not comprising metal oxide. Example materials and constructions for a multi-resistive state region comprising one or more layers including a programmable metal oxide-comprising material are described and disclosed in U.S. Pat. Nos. 6,753,561; 7,149,108; 7,067,862; and 7,187,201, as well as in U.S. Patent Application Publication Nos. 2006/0171200 and 2007/0173019. Further as is conventional, multi-resistive state metal oxide-comprising materials encompass filament-type metal oxides, ferroelectric metal oxides and others, and whether existing or yet-to-be developed, as long as resistance of the metal oxide-comprising material can be selectively changed.
The programmable material may comprise memristive material. As an example, such material may be statically programmable semiconductive material which comprises mobile dopants that are received within a dielectric such that the material is statically programmable between at least two different resistance states. At least one of the states includes localization or gathering of the mobile dopants such that a dielectric region is formed and thereby provides a higher resistance state. Further, more than two programmable resistance states may be used. In the context of this document, a “mobile dopant” is a component (other than a free electron) of the semiconductive material that is movable to different locations within said dielectric during normal device operation of repeatedly programming the device between at least two different static states by application of voltage differential to the pair of electrodes. Examples include atom vacancies in an otherwise stoichiometric material, and atom interstitials. Specific example mobile dopants include oxygen atom vacancies in amorphous or crystalline oxides or other oxygen-containing material, nitrogen atom vacancies in amorphous or crystalline nitrides or other nitrogen-containing material, fluorine atom vacancies in amorphous or crystalline fluorides or other fluorine-containing material, and interstitial metal atoms in amorphous or crystalline oxides. More than one type of mobile dopant may be used. Example dielectrics in which the mobile dopants are received include suitable oxides, nitrides, and/or fluorides that are capable of localized electrical conductivity based upon sufficiently high quantity and concentration of the mobile dopants. The dielectric within which the mobile dopants are received may or may not be homogenous independent of consideration of the mobile dopants. Specific example dielectrics include TiO2, AlN, and/or MgF2. Example programmable materials that comprise oxygen vacancies as mobile dopants may comprise a combination of TiO2 and TiO2-x in at least one programmed resistance state depending on location of the oxygen vacancies and the quantity of the oxygen vacancies in the locations where such are received. An example programmable material that comprises nitrogen vacancies as mobile dopants is a combination of AlN and AlN1-x, in at least one programmed state depending on location of the nitrogen vacancies and the quantity of the nitrogen vacancies in the locations where such are received. An example programmable material that comprises fluorine vacancies as mobile dopants may is a combination of MgF2 and MgF2-x in at least one programmed resistance state depending on location of the fluorine vacancies and the quantity of the fluorine vacancies in the locations where such are received. As another example, the mobile dopants may comprise aluminum atom interstitials in a nitrogen-containing material.
Still other example programmable materials include organic materials and organic-metal complexes, such as Bengala Rose, AlQ3Ag, Cu-TCNQ, DDQ, TAPA, fluorescine-based polymers, poly(vinylidene fluoride-ran-trifluroethylene), rotaxanes, catenanes, amino diethylphenylnitrobenzenethiolate, amorphous carbon, and graphene.
The programmable material, as well as other materials disclosed herein, may be deposited by any existing or yet-to-be-developed technique(s). Examples include vapor phase deposition (i.e., chemical vapor phase deposition, atomic layer deposition, and/or physical vapor deposition) and/or liquid phase deposition, either of which may be selective or non-selective to one or more underlying materials. In example liquid-phase depositions, surface mediated transport (capillarity) and or electrokinetic flow may occur. Wetting agents, surfactants, or other surface modification agents may or may not be used. Further and regardless of deposition method, any deposited material may be subsequently treated, for example annealed or irradiated. Such treatment(s) may or may not induce a chemical reaction that produces the desired memory cell material from deposited precursor materials.
Programmable material 32 may or may not be subsequently patterned after its formation. In one example, programmable material 32 may be blanketly deposited (i.e., non-selectively) over substrate 12, and subsequently planarized back relative to an outer surface of second electrode lines 28. The construction of
As an alternate example, programmable material may be formed by selective growth from at least one of the first and second electrode lines. For example, the embodiment of
Referring to
The processing as described above to produce any of the
Tier 44 and/or any additional tier fabricated outwardly thereof, may be formed with processing analogous to that shown with respect to tier 42, or otherwise. In one embodiment, the removing of sacrificial material and the forming of programmable material (and optionally select device material) for a respective individual of the vertically stacked tiers during fabrication of the array may occur one tier at a time. Alternately, such removing of the sacrificial material and the forming of programmable material (and optionally select device material) for the individual tiers may occur for multiple tiers at the same time, or for all tiers at the same time.
Individual tiers of a multiple stack of tiers of memory cells need not be of the same construction or processed the same relative one another, and may occur in accordance with any of the processing described above, or otherwise, with respect to the example embodiments of
Additional embodiments of a method of forming an array of vertically stacked tiers of nonvolatile memory cells are next described with reference to
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In one embodiment, a plurality of horizontally oriented global second electrode lines may be formed. Conductive material within individual of the vertically oriented openings may comprise a local vertically oriented second electrode line that extends from and in current conductive connection with individual of the horizontally oriented global second electrode lines. For example,
One or more select devices may additionally be formed with respect to any of the embodiments described above with respect to
Embodiments of the invention encompass methods of forming a nonvolatile memory cell, with the above-described embodiments showing methods of forming a plurality of such cells. Regardless, such method of forming a memory cell comprises forming a first electrode, a second electrode, and providing sacrificial material between the first electrode and the second electrode. The sacrificial material is exchanged with programmable material to be used in the memory cell. In one embodiment, the sacrificial material may be exchanged with select device material in addition to exchanging the sacrificial material with programmable material. In one embodiment, the first electrode is formed before forming the second electrode, and the sacrificial material is provided by depositing such after forming the first electrode and prior to forming the second electrode. In one embodiment, the sacrificial material is deposited before depositing any second electrode material. Regardless, in one embodiment, no programmable material is provided between the first and second electrodes before exchanging the sacrificial material with programmable material.
In one embodiment, the first electrode and the second electrode are formed to be horizontally oriented. The embodiments of
In one embodiment, the second electrode is formed elevationally outward of the first electrode and the exchanging comprises removing the sacrificial material from between the first and second electrodes and subsequently depositing the programmable material elevationally under the second electrode and elevationally over the first electrode. The embodiments of
In one embodiment, the first and second electrodes are laterally oriented relative one another where such cross, with the sacrificial material being received laterally there-between. The exchanging of sacrificial material with programmable material comprises removing the sacrificial material from between the first and second electrodes and subsequently depositing the programmable material laterally between the first and second electrodes. The embodiments of
As described above, an array of individual memory cells may or may not comprise a select device within individual memory cells. Control and other circuitry may be received outside of or proximate edges of the array for reading, writing, and otherwise accessing the individual memory cells located where the individual electrode lines cross. However, additional circuit structures may be included within the individual memory cells.
Accordingly, in connection with the above described example embodiment of
In compliance with the statute, the subject matter disclosed herein has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the claims are not limited to the specific features shown and described, since the means herein disclosed comprise example embodiments. The claims are thus to be afforded full scope as literally worded, and to be appropriately interpreted in accordance with the doctrine of equivalents.
Claims
1. A method of forming a nonvolatile memory cell, comprising:
- forming a first electrode of the memory cell;
- forming a second electrode of the memory cell;
- providing sacrificial material between the first electrode and the second electrode; and
- exchanging the sacrificial material with programmable material of the memory cell.
2. The method of claim 1 wherein,
- the first electrode is formed before the second electrode; and
- providing the sacrificial material comprises depositing sacrificial material after forming the first electrode and prior to forming the second electrode.
3. The method of claim 1 wherein,
- the first electrode is formed before the second electrode;
- providing the sacrificial material comprises depositing sacrificial material;
- forming the second electrode comprises depositing second electrode material; and
- the sacrificial material is deposited before depositing the second electrode material.
4. The method of claim 1 comprising forming the first electrode and the second electrode to be horizontally oriented.
5. The method of claim 1 comprising forming one of the first and the second electrodes to be horizontally oriented and the other of the first and second electrodes to be vertically oriented.
6. The method of claim 5 wherein the first electrode is formed before the second electrode, and the first electrode is horizontally oriented.
7. The method of claim 1 wherein the sacrificial material is electrically insulative.
8. The method of claim 1 wherein the sacrificial material is electrically conductive.
9. The method of claim 1 wherein the sacrificial material is semiconductive.
10. The method of claim 1 being void of programmable material between the first and second electrodes before the exchanging.
11. The method of claim 1 wherein the first electrode, the second electrode, and the sacrificial material are formed over a substrate; the exchanging comprising removing the sacrificial material from between the first and second electrodes and subsequently blanketly depositing the programmable material over the substrate.
12. The method of claim 1 wherein the exchanging comprises removing the sacrificial material from between the first and second electrodes and subsequently selectively growing the programmable material from at least one of the first and second electrodes.
13. The method of claim 12 comprising selectively growing the programmable material from both of the first and second electrodes.
14. The method of claim 12 comprising selectively growing the programmable material from only one of the first and second electrodes.
15. The method of claim 1 wherein the memory cell comprises a select device received between the first and second electrodes; and further comprising:
- exchanging the sacrificial material with select device material in addition to exchanging the sacrificial material with programmable material.
16. The method of claim 15 comprising forming the select device material before forming the programmable material.
17. The method of claim 16 wherein the exchanging with programmable material comprises removing the sacrificial material from between the first and second electrodes and subsequently selectively growing the programmable material from only one of a) the select device material; or b) only one of the first or second electrodes.
18. The method of claim 17 wherein the selectively growing is from the select device material.
19. The method of claim 17 wherein the selectively growing is from only one of the first or second electrodes.
20. The method of claim 1 wherein the second electrode is formed elevationally outward of the first electrode, the exchanging comprising removing the sacrificial material from between the first and second electrodes and subsequently depositing the programmable material elevationally under the second electrode and elevationally over the first electrode.
21. The method of claim 1 wherein the first and second electrodes are laterally oriented relative one another where such cross with the sacrificial material received laterally there-between; the exchanging comprises removing the sacrificial material from between the first and second electrodes and subsequently depositing the programmable material laterally between the first and second electrodes.
22. A method of forming an array of nonvolatile memory cells, comprising:
- forming a plurality of horizontally oriented first electrode lines and a plurality of horizontally oriented second electrode lines elevationally outward of the first electrode lines;
- providing sacrificial material elevationally between the first and second electrode lines where such cross;
- removing the sacrificial material from between the first and second electrode lines where such cross; and
- after the removing, forming programmable material elevationally between the first and second electrode lines where such cross.
23. The method of claim 22 wherein said first electrode lines, said second electrode lines, and said programmable material there-between comprise a single tier of multiple vertically stacked tiers of nonvolatile memory cells of the array.
24. The method of claim 23,
- wherein said multiple vertically stacked tiers during fabrication of the array individually comprise: a respective plurality of horizontally oriented first electrode lines; a respective plurality of horizontally oriented second electrode lines elevationally outward of the respective first electrode lines, and sacrificial material elevationally between the respective first and second electrode lines where such cross; and
- further comprising: removing the sacrificial material from between the respective first and second electrode lines where such cross for individual of the respective vertically stacked tiers during fabrication of the array; and after said removing for individual of the respective vertically stacked tiers during fabrication of the array, forming programmable material between the respective first and second electrode lines where such cross for individual of the respective vertically stacked tiers during fabrication of the array.
25. The method of claim 24 comprising conducting said removing and forming of programmable material for respective individual of the vertically stacked tiers during fabrication of the array one tier at a time.
26-35. (canceled)
Type: Application
Filed: Dec 27, 2010
Publication Date: Jun 28, 2012
Patent Grant number: 8431458
Inventors: Scott E. Sills (Boise, ID), Gurtej S. Sandhu (Boise, ID)
Application Number: 12/979,189
International Classification: H01L 21/02 (20060101);